With the recent progress in the functions of image recording means and image display means, high-quality color copying machines, color printers, and the like have become rapidly popular. In the field of image communication apparatuses, color facsimile apparatuses and the like have been developed. Communication schemes for such color facsimile apparatuses are being standardized as ITU-T recommendations such as T30, T40, T42, and T81. In addition, as an encoding scheme for such color images, T81 of JPEG (Joint Photographic Expert Group) is used.
In a color facsimile apparatus standardized as the ITU-T recommendation T30, as minimum requirements for color image data, a width in the main scanning direction: A4 and a resolution: 200 dpi are defined. As options, a width in the main scanning direction: B4/A3 and a resolution: 100/300/400 dpi can be selected.
As color printing schemes, a thermal sublimation transfer scheme, thermal fusion transfer scheme, electrophotographic scheme, ink-jet scheme, and the like are known. The respective schemes have merits and demerits in terms of color image reproducing capability. In addition, the color reproducing capability varies depending on the type of printing paper to be used, the type of ink, and the arrangement of an apparatus.
There are growing user needs for transmission of an image having a size equivalent to, for example, a snapshot by using such a color facsimile apparatus. With a conventional facsimile apparatus, however, even when an image of such a size is transmitted, since the minimum size of an image that can be transmitted/received is A4, the image is transmitted as an A4-size document. For this reason, the receiving apparatus prints even the image of the snapshot size on an A4-size printing sheet, resulting in a waste of the printing sheet. In addition, an expensive, special printing sheet is used to print a sharp color image. In this case, an expensive printing sheet is wasted.
Furthermore, when a small-size image like the one described above is transmitted in A4 size, even a meaningless data portion is produced as image data. As a consequence, useless transmission data increases in amount, and the communication time is prolonged accordingly, resulting in an extra communication cost.
In the color facsimile procedure according to the T30 recommendation, a quantization table that determines image quality in compressing (JPEG-compressing) a color image is also sent to the receiving apparatus. This means that the reproduction quality of image data to be transmitted can be arbitrarily determined on the transmitting side. For this reason, for example, even if the color reproducing capability of the apparatus on the receiving side is low, the quality of an image generated on the transmitting side may become excessively high. In such a case, the amount of unnecessary transmission data increases, and hence the corresponding communication time and cost are wasted.